How Do You Measure an Arched Window for Blinds?

Arched windows add architectural interest and natural light, but they also create challenges when fitting blinds. A fraction of an inch off can cause gaps, uneven operation, or a treatment that simply does not fit. Accurate measurement ensures your investment in blinds pays off with smooth performance, proper coverage, and a finish that complements the window’s unique shape.

For homeowners in Toronto and across Canada, where custom window treatments are often preferred for energy efficiency and style, understanding how to measure correctly is essential before ordering.

Tools You’ll Need

Measuring arched windows requires more precision than standard rectangular frames. Gather the following tools before you begin:

• A steel measuring tape (avoid fabric tape for better accuracy)
• A step ladder if the window is tall
• A carpenter’s level to check symmetry
• A pencil and a notepad or a digital device for recording numbers
• A flexible curve ruler or template material for tracing complex arches

Having these tools ready will allow you to record accurate data on the first attempt.

Related Article: Can You Put Blinds on Arched Windows? Yes—Here’s How

Step 1: Determine the Mount Type

Before measuring, decide whether the blinds will be mounted inside the window frame or outside it.

• Inside mount: Offers a clean, built-in look. The blinds fit snugly within the window recess, following the natural curve of the arch. This requires the most accurate measurements.
• Outside mount: Installed on the wall or moulding above the window. It provides full coverage and can visually enlarge the window, but may conceal trim detail.

Your choice of mount will influence every measurement that follows.

Step 2: Measure the Base Width

For any arched window, start with the width across the bottom, where the arch meets the straight sides. Measure from left to right inside the frame (for inside mount) or across the outside edges (for outside mount). Record this as the base width.

Take the measurement at three points — bottom, centre, and top of the rectangular portion of the window — to confirm consistency. Use the narrowest width for ordering inside-mounted blinds.

Step 3: Measure the Height

Next, measure from the centre of the base straight up to the highest point of the arch. This is your arch height. Be sure the tape measure is vertical and not angled, as even slight deviations can distort the final fit.

For non-perfect arches, you may want to record two additional height measurements, one on the left and one on the right, where the arch starts to curve. This will help identify asymmetry.

Related Article: Best Blinds for Large Windows

Step 4: Identify the Arch Type

Not all arches are alike, and identifying the type is critical to choosing the right blinds. Common shapes include:

• Perfect arch: The height is exactly half the width.
• Eyebrow arch: The height is less than half the width, creating a shallow curve.
• Elliptical arch: More elongated, with height greater than half the width.
• Quarter arch: A window shaped like one quarter of a circle.

Knowing the type helps your blind manufacturer or installer recommend the correct product.

Step 5: Trace the Curve

For highly custom blinds, such as wood or faux-wood options, you may be asked to provide a tracing. Tape a piece of stiff paper or cardboard to the window frame, then trace the exact curve of the arch with a pencil. Cut out the template and mark it with the width and height. This can be sent to your blinds supplier to ensure an exact match.

Step 6: Double-Check for Symmetry

Older homes in Toronto and other cities often have arched windows that are not perfectly symmetrical. Using a level, verify that both sides of the arch rise at the same angle. Record left and right side measurements separately. If they differ, your installer will use the smaller measurement to ensure fit.

Special Considerations for Different Blind Types

The type of blind you choose affects how the measurements are applied.

• Cellular shades: Popular for arched windows due to their flexibility. They can be made as fixed fan-shaped inserts or as operable shades. Measurements must be exact, especially for inside mounts.
• Zebra blinds: Typically suited for the rectangular portion of arched windows, with a fixed sunburst insert for the arch.
• Wood and faux-wood blinds: Require templates for accurate cutting due to rigid materials.
• Motorized blinds: Precision is even more critical, as misalignment can interfere with automated operation.

Related Article: How to Fix Common Zebra Blinds Problems

Common Mistakes to Avoid

1. Using soft measuring tape: This can stretch and produce inaccurate readings.
2. Measuring only once: Always measure at least twice and from different points.
3. Ignoring mount type: Inside vs outside mount changes the required width and height.
4. Forgetting depth: For inside mounts, record the depth of the window frame to ensure the blinds fit flush.
5. Overlooking trim details: Ornate mouldings may require adjustments to outside-mount measurements.

Why Professional Measurement May Be Worth It

While do-it-yourself measurement is possible, many homeowners prefer to have professionals handle it. Blinds Toronto offers free in-home consultations. 

A trained specialist brings the right tools, measures every arch precisely, and discusses options for materials, colours, and automation. This ensures that when the blinds arrive, they fit perfectly and enhance the window’s design rather than fighting against it.

Considering the investment involved, professional measurement can prevent costly errors.

Design Tips for Arched Windows with Blinds

Measurement is the foundation, but design choices complete the look. Keep these points in mind:

• Highlight the curve: Fixed fan-shaped blinds or cellular shades can showcase the arch instead of hiding it.
• Balance light and privacy: Combine an operable shade for the lower portion with a fixed insert in the arch for flexibility.
• Match the décor: Select colours and textures that echo your existing interior design, whether modern, traditional, or transitional.
• Consider energy savings: Cellular shades provide insulation, reducing heat loss in winter and solar gain in summer.

Step-by-Step Example

Imagine an eyebrow arch window 60 inches wide at the base and 18 inches high at the centre. Here’s how the process would look:

1. Decide on an inside mount.
2. Measure the base width at three points: 60, 60, and 59.75 inches. Use the narrowest—59.75 inches.
3. Record the centre height: 18 inches.
4. Note that height is less than half of the width, confirming an eyebrow arch.
5. Create a template to capture the shallow curve.
6. Verify both sides measure evenly from base to the start of the curve.

With these numbers, your blind supplier can create a custom cellular shade insert that fits seamlessly.

Related Article: Step-by-Step Guide to Measuring Windows for Blinds Installation

Getting It Right the First Time

Arched windows deserve precision. Careful measurement avoids disappointment and ensures the blinds complement the architecture. By following the steps outlined — measuring width, height, identifying arch type, tracing curves, and confirming symmetry — you can provide your installer with accurate data or confidently measure yourself if ordering custom blinds online.

For those who prefer assurance, scheduling a consultation with a local expert is often the simplest route.

Elevating Your Home with Properly Fitted Arched Window Blinds

An arched window blind that fits properly does more than block light. It respects the architecture, adds character to the room, and improves comfort. Whether you take the measurements yourself or rely on a professional, accuracy is the key to success.

Ready to transform your arched windows? Contact us or book a free consultation and expert measurement today.